The present invention relates to a powertrain for a hybrid vehicle using hydraulic power as an energy storage device, and a hybrid vehicle equipped with such a powertrain.
A conventional hybrid vehicle uses an internal combustion engine as the main motorization, and a hydraulic machine connected to the combustion engine, which can function as a motor or a pump to either charge hydraulic pressure accumulators, or to supply mechanical power to drive wheels of the vehicle by drawing energy from the accumulators.
In this way, the hydraulic machine can be used as a pump during the braking phases to recharge the pressure accumulators, thereby recovering the kinetic energy of the vehicle. During the acceleration phases, the hydraulic machine can also be used as a motor by drawing pressurized fluid from the accumulator to supply mechanical power in addition to the power supplied by the combustion engine.
The use of the energy storage device optimizes the operation of the combustion engine and reduces its consumption and polluting emissions.
A known refinement of these hybrid vehicles, in particular disclosed in document US-A1-20090036248, includes a first hydraulic machine connected to the combustion engine, and a second hydraulic machine connected to one element of a planetary gear system, while one of the two other elements of the planetary gear system is connected to the drive wheels of the vehicle and the other element to the combustion engine.
In this arrangement, the two hydraulic machines can be used in parallel operating mode, whereby the hydraulic machines and the combustion engine can simultaneously drive the drive wheels of the vehicle through a mechanical power transmission.
However, this arrangement is not conducive to serial operating mode because the two hydraulic machines are permanently mechanically coupled to each other. On the one hand, this allows recharging of the pressure accumulators by the combustion engine through a first hydraulic machine. On the other hand, this allows use of the stored energy in independent manner to provide traction to the vehicle through the second hydraulic machine at suitable rotational speeds for each machine, which can be regulated independently to optimize the operating points.